The UMTS terrestrial radio access time division duplex (UTRA TDD) mode is based on a combination of code division multiple access (CDMA) and hybrid time division multiple access (TDMA). UMTS is an acronym for universal mobile telecommunication system as will be understood by persons skilled in the art.
Reliable operation in the UTRA TDD mode, incorporating the combined TD-CDMA multiple access scheme, requires synchronisation between base stations within a compliant telecommunications system. Moreover the mode also requires the provision of position information for the mobile stations affiliated to each base station. Synchronisation between base stations is also desirable in order to maximise system capacity. To these ends, the synchronisation of base stations must be achieved at the levels of time slots, frames and multi-frames, where a multi-frame is a repeating cycle of a number of frames.
One known mechanism for synchronising the base stations is to equip each base station with a global positioning system (GPS) receiver. However, this is not always appropriate or even possible; for example, an area of deployment may be shadowed from the GPS constellation of satellites by tall buildings. For this and other reasons, alternative mechanisms for synchronising the base stations are required.
In an alternative mechanism, the base stations are synchronised over the backhaul network; the network which enables base stations to switch mobile communications into public telephone networks or the internet. However, if this mechanism is implemented according to a packet protocol (for example, internet protocol (IP) or asynchronous transfer mode (ATM)), then synchronisation will only be possible to a coarse accuracy.